1. Field of the Invention
The present invention relates to an apparats having an optical window or windows, such as an underwater camera arranged to be usable for underwater photography.
2. Description of Related Art
When an underwater camera is in the atmosphere, optical members forming an optical system and air sealed inside the camera have about the same temperature as the temperature of the atmosphere. Generally, the temperature of water is lower than the temperature of the atmosphere. Therefore, when the underwater camera is placed in the water, an optical member such as an optical window that comes in contact with water is cooled. Then, an aqueous vapor is sometimes generated within the camera and sticks to the inner surface of the optical member to fog the optical member. Such a fogged optical member then has some adverse effects on taking a picture or making an observation. Accordingly, in the conventional underwater camera, such fogging is prevented by arranging optical members (sealing window members) Q that come into contact with water to be in a double-paned structure, as shown in FIG. 3. Incidentally, in FIG. 3, reference numeral 1 denotes a photographing optical system, reference numeral 2 denotes a viewfinder optical system, and reference numeral 3 denotes a film surface, which is set on the image forming plane of the photographing optical system 1.
However, in the conventional structure of the underwater camera such as that shown in FIG. 3, the number of parts of the sealing window members Q is inevitably increased. Therefore, the size and cost of the conventional underwater camera are increased by the arrangement mentioned above.